The two things that you spend most of your time doing as a programmer — coding and debugging — are made noticeably easier and more fun by that combination of Smalltalk language and IDE. The language syntax is small, powerful, expressive, introspective. The entire stack (and libraries, and IDE) is written in Smalltalk (turtles all the way down), and you have access to the source code, allowing you to study and extend all operations, basic and complex. The code organization — explicit, first-class visual IDE support for packages, classes, protocols (groupings of methods by intended use) and methods — is extremely helpful.

Follow the link and see what he says about the debugger - non-Smalltalkers often miss the power of the debugger in Smalltalk.